Browsing by Subject "cementyt"
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Item type:Doctoral Dissertation, Access status: Restricted , Rola cementytu w procesie pękania staliwa L200HNM(Data obrony: 2008-07-08) Rożniata, Edyta
Wydział OdlewnictwaThe chromium - nickel - molybdenum cast steel of ledeburite class is mainly used for working mili rolls. These rolls are one of the most expensive instruments employed in mechanical working of metals. A very serious problem for large-size cast rolls (including rolls madę of cast steels of ledeburite class) is the risk of their fracture. Probable cause of cast steel rolls fracture is the presence in their structure of continuous network of hypereutectoid cementite and transformed ledeburite precipitated along prior grain boundaries of former austenite and precipitates of hypereutectoid cementite in structure of Widmannstätten type. The network, formed in the roll's structure just after casting is a way for easy propagation of the fractures and decreases the mechanical properties of the rolls, especially fracture toughness, so important for the users of that instrument. That is why, therefore within the framework of the paper an attempt of refinement of prior austenite grain, evaluation of the influence of the refinement and cooling rate on the hypereutectoid cementite morphology and fracture toughness of G200CrNiMo4-3-3 cast steel. To reach the aims of the work and prove formulated thesis investigated materials were underdone to wide researching and complex analysis. Research of G200CrNiMo4-3-3 cast steel included metallographic and fractographic analysis and fracture toughness research (impact strength, stress intensity factor $K_{Ic}$ and hardness). However the most important thing was to create fine substructure (advantageous from the tribologic properties) with subtle network of partially coagulated hypereutectoid cementite by application of incomplete „normalizing" annealing for test cast steel.Item type:Doctoral Dissertation, Access status: Restricted , Sferoidyzacja cementu w perlicie stali eutektoidalnej(Data obrony: 2006) Skowronek, Tadeusz
Wydział Inżynierii Metali i Informatyki PrzemysłowejItem type:Doctoral Dissertation, Access status: Restricted , Związek między rekrystalizacją ferrytu i koagulacją dyspersyjnej fazy węglikowej w stali $Fe - 0.67\% C$(Data obrony: 2009) Matusiewicz, Piotr
Wydział Inżynierii Metali i Informatyki PrzemysłowejKinetics of $Fe_{3}C$ particle coarsening in $Fe-0.67\%C$ steel for two (A, B) different microstructures (spheroidite) with similar dispersion, but different matrix (ferrite) grain size and particles distribution was investigated experimentally. In microstructure A, formed by hardening with subsequent tempering, the particles are mainly on fine matrix grain (subgrain) boundaries (in situ recrystallization of ferrite). In microstructure B, formed by recrystallization after cold work ($10\%$), the particles are mainly inside grains of coarse-grained matrix (discontinuous recrystallization of ferrite). During anneling (680, 700 i $715^{\circ}C$; 800 hours) microstructure (A, B) morphology is preserved; steel microstructure determine the particle coarsening rate, it is lower in microstructure B; the grain growth occurs in microstructure A. Analysis of empirical kinetic functions with LSW theory suggest that higher particle coarsening rate in microstructure A results from higher diffusivity of $Fe$ along the matrix grain boundaries. Lower particle coarsening rate in microstructure B results from matrix diffusion of $C$ and $Fe$. In microstructure A particle coarsening controls the grain growth (particle disappearance makes grain boundary migration possible). Empirical distributions of cementite particle size are similar to the Weibull distribution.